The gas turbines used to produce electrical power emit an exhaust stream. That exhaust stream is of a relatively high noise level such that it is desirable to quiet the noise level to more acceptable levels. Traditionally, the quieting has been done by what is known as a "silencer" or a "silencing system" which serves to attenuate the sound. The silencing system generally consists of a silencer chamber attached to the exhaust plenum downstream from the gas turbine. Within the silencing chamber a series of silencer panels are arrayed. The silencer panels are generally of a rectangular shape and spaced apart. The size and thickness of the silencer panels as well as their spacing serve to determine how much sound attenuation is accomplished and at what frequencies.
Generally, the silencer panel is designed to be extremely rigid to take the stresses encountered in the gas turbine exhaust stream. These include a very turbulent gas stream and an extreme of temperatures ranging from sub zero, such as prior to start up in a cold climate, to 1,250.degree. F., when the system reaches operating temperature. Likewise, the system can cycle through these temperature extremes such as when the gas turbine is shut down for maintenance. Because of the extremes of temperature, the silencer panel expands and contracts. The silencer panel is full of acoustical insulation which also acts as a thermal insulator to the internal structure of the panel. Therefore, the interior of the panel expands and contracts at a different rate than the exterior. This can cause high localized stresses and consequently, a short life expectancy for the silencer panel.
The silencer panels have typically been made out of stainless steel such as a ASTM type 409. Newer technology for gas turbines has resulted in higher firing temperatures. These higher firing temperatures have required different material to take the higher temperatures. For example, austenitic stainless steel is often used in place of type 409 stainless steel. The austenitic stainless steel has a higher thermal coefficient of expansion and hence, accentuates the localized thermal stresses during cycling of the system, and with current designs would be expected to lead to an even shorter life span for the silencer panels.